Full wave reversible polarity magnetic amplifier



Sept. 27, 1960 c. B. HOUSE 2,

FULL WAVE REVERSIBLE POLARITY MAGNETIC AMPLIFIER Filed June 12, 1956 INVENTOR CLARENCE 8 HOUSE BY 4/ WW MW ATTORNEY} United States Patent FULL WAVE REVERSIBLE POLARITY MAGNETIC AMPLIFIER Clarence B. House, Arlington, Va., assignor to the United States of America as represented by the Secretary of the Navy Filed June 12, 1956, Ser. No. 591,001

6 Claims. (Cl. 323-89) (Granted under Title 35, U.S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates generally to magnetic amplifiers and more specifically to full wave reversible polarity magnetic amplifiers.

The basic. half cycle response time magnetic amplifier is essentially a half wave circuit inasmuch as it delivers power to, a load on one half cycle and resets its core according to a control signal on the alternate half cycle. Many circuits have been devised to provide full wave magnetic amplifier operation and deliver power to a load on successive half cycles. However, many new difiiculties are introduced by full wave magnetic amplifier operation. These are occasioned principally by the fact that at least one core is being reset while another is on its gating cycle and the heavy flow of gating current is very likely to be coupled back to influence the resetting core and'thus introduce serious distortion to the output voltage.

Additional difficulties arise with reversible polarity circuits having two polarity sensitive cores operating on each gating half cycle. Such circuits are likely to carry very heavy currents should both cores saturate during the gating half'cycle, the heavy currents not only may damage the circuit components but also represent a waste of energy. The components may be protected by limiting resistances but the energy dissipated by such resistances is'still wasted.

It is therefore anobject of this invention to provide a full'wave reversible polarity magnetic amplifier having none of the above disadvantages.

It is another object of this invention to provide a reversible polarity magnetic amplifier which minimizes current with all cores saturated.

It is another object of this invention to provide a magnetic amplifier which automatically resets the cores to provide optimum control phase current for servo motor operation.

It is another object of this invention to provide a full wave magnetic amplifier in which the resetting windings are decoupled from the gating windings.

It is another object of this invention to provide a parallel feed control circuit for a full wave reversible polarity magnetic amplifier which is not eifected by the gating current.

Other objects and advantages of this invention will become apparent upon a consideration of the following description and accompanying drawings wherein similar characters of reference indicate similar components.

In the drawings:

Fig. 1 is a full wave reversible polarity magnetic am- 'plifier illustrating the minimum saturation current and automatic reset features of this invention.

Fig. 2 is a variant embodiment of this invention showing the circuit of Fig. 1 with a parallel feed control circuit with integrated reset circuit.

Patented Sept. 27, 1960 ice Referring now to Fig. 1 in detail, a four core magnetic amplifier circuit is shown in which, for the connections and voltage polarities shown, cores 12 and 14 are on their gating half cycle and cores 11 and 13 are resetting. Each of the cores has square hysteresis loop characteristics. AC. power is supplied to the circuit through a pair of windings 15, shown on separate cores, whichenergize center tapped secondaries 16 and 17. Windings 16 and 17 could be wound on a single core thus requiring only one winding 15. Winding 16 is connected to a pair of diodes 18 and 19 to the load windings 20 and 21 of cores 11 and 12 respectively. The other end of load windings 20 and 21 are connected together at common terminal 22. Similarly, winding 17 is connected to a pair of rectifiers 23 and 24 to load windings 25 and 26 of cores 13 and 14 respectively. The other end of load windings 25 and 26 are connected to the common terminal 22. Each of the pairs of rectifiers 18 and 19, and 23 and 24, are polarized so that current cannot flow in both rectifiers of a pair on any half cycle but can flow in the corresponding rectifier of each pair during the same half. cycle. The center taps of each of cores 16 and 17 are connected across the load resistor 27 and also across the center taped primary 28 of transformer 29. The center tap of winding 28 is returned through a compensating resistance 30 to common terminal 22. Because of the polarities of the rectifiers, load current from either of windings 16 and 17 can flow through only half the winding on any half cycle, through its adjacent rectifier and load winding and returning to the transformer winding center tap through one half of winding 28. Control windings 31, 32, 33 and 34 are wound on cores 11 through 14, respectively, and are serially connected with the polarities shown so that cores 11 and 13 are differentially reset and cores 12 and 14 are also differentially reset. The control voltage is supplied to the series connection of control windings as shown at E To prevent the output pulse from coupling through a gating core to its control winding and hence to the series control circuit, a secondary winding 35 is placed on transformer 29 to introduce a feedback voltage to oppose the output voltage transformed to the control circuit from a gating load winding. Resistance 30 is selected in value to develop half the output voltage across itself. By so doing the output voltage developed in the half of winding 28 which is developed by autotransformer action in the half of winding 28 which is not carrying load current will be opposed by the voltage developed across resistance 30 and not introduced to the load windings of the resetting cores. For example, presuming that the load current is flowing in the upper half of winding 28, the voltage induced by transformer action into the lower half of winding 28 will be impressed in series with resistance 30, across the center tap of winding 17 and common terminal 22. It will be seen therefore that this voltage is impressed across load windings 25 and 26. By developing an equal and opposite voltage across resistance 30 the autotransformed voltage is fully opposed and the centertap of winding 17 and common terminal 22 are placed at equal potential. A more detailed description of the series control circuit, feedback winding 35, and compensating resistance 30 may be found in the copending application of D. G. Scorgie for Push-Pull Magnetic Amplifier now issued as U.S. Patent No. 2,885,631.

In considering the operation of the circuit of Fig. l as thus far described, it is important to note that cores 11 and 13 and cores 12 and 14 are paired for gating or resetting. This is accomplished by polarizing rectifiers 18, 19, 23 and 24 as shown. As a result the maximum uncontrolled flow on any gating half cycle is minimized. For example, for the polarities shown with the right hand ends of windings 16 and 17 positive cores 12 and 14 are on their gating half cycle since rectifiers 19 and 24 are capable of supplying load current, whereas rectifiers 18 and 23 are blocking. Should both cores 12 and 14 reach saturation during the gating half cycle due to neither a small differential reset or the lack of any control signal on the previous reset half cycle, windings 21 and 26 will introduce no impedance to the flow of current and heavy current will flow from winding 16 through rectifier 19, winding 21, resistance 30, the upper half of winding 28 and back to winding 16, the other heavy current path will set up from winding 17 through rectifier 24, winding 26, resistance 30, the lower half of winding 28 and back towinding 17. These two heavy current paths will flow in opposite directions through winding 28 so that no voltage will be delivered to the load, they will be flowing in the same direction through resistance 30 which will therefore serve not only as a current limiting resistance but also as an opposing voltage source since the voltage developed across resistance 30 from one of the heavy current paths will be in opposition to the flow of current in the other heavy current path due to the parallel connection. 'I'hus current limiting is provided by resistance 30 which was already present in the circuit and serving an important function, and secondly the two heavy current paths tend to oppose each other by their parallel connection across resistance 30.

An important consideration in the development of control circuitry is the desired shape of the output waveform. Measurements show that in two phase servo motor operation, the component of control phase current which is eifeetive in producing motor torque is that fund-amen-tal frequency component which is a 90 angular relationship with the reference phase current. This limitation requires current pulses in the control phase to center about the peak voltage point rather than occurring near the end of the gating half cycle. To obtain the desired phase relationship, at zero signal voltage the gatingcores should simultaneously saturate at 90. If the two cores saturate at the same instant, the currents through the two halves of output transformer winding 28 will be of equal magnitude and opposite direction and no voltage will appear across the load. Upon introduction of a signal, the two resetting cores will be difieren- I On the next gating half cycle, one core tially reset. will advance its firing angle a certain number of degrees and the other core will have its firing angle retarded a like amount. During the period subsequent to former 29. By autotransformer action twice this voltage will appear across the load. For these conditions to obtain, means must be provided to set the no signal flux level in the resetting cores at such a point to pro- In the c-irduce firing at the 90 point as described. cui-t of Fig. 1, the desired degree of reset is supplied to the resetting cores through their load windings by the addition of bypass resistors 36, 37, 38 and 39 in parallel with rectifiers 18, 19, 23 and 24, respectively. The

reacting upon the saturable cores because of stored energy feedback.

-In order to eliminate all reaction of the gating cores on the resetting cores, the parallel food type of control circuit shown in Fig. 2 has been provided. Referring now to Fig. 2 in detail, the gating circuits remain as in the series feed amplifier of Fig. 1 except for the elimination of the by-pass resistors which establish the initial one cores gating and prior to the other cores firing a voltage will appear across one half of the output transcore reset bias. The reset bias which will give firing angle on all cores in the absence of signal is now supplied by a volt-age E to be further described below. Each pair of control windings 31 and 33, and 32 and 34 are connected in parallel across a center tapped winding 40 of a control signal input transformer 41. The control signal E is supplied to another winding 42 of transformer 41. Each of the pairs of control windings are serially connected with "their common terminals 43 and 44 returned to the center tap 45 of winding 40. The connection of each of the control windings 31 through 34 to transformer winding 40 is through a separate rectifier designated 46 through49, respectively. These rectifiers are poled to prevent simultaneous conduction in both control windings of a pair. The return of control Winding junctions 43 and 44 to terminal 45 is through bias source E and also through a pair of switching rectifiers 50 and '51, respectively. Each of reetifiers 50 and 51 are biased by voltage source E and a pair of current limiting resistors 52 and 53, respectively.

Considering now the operation of the parallel feed control circuit with respect to voltage source E and E each of the latter sources are alternating voltages alternating synchronously with the supply frequency B The phasing of the voltage sources is best described by showing polarities in the circuit of Fig. 2 where, for the connections and polarities shown, cores 11 and 13 will be resetting while cores 12 and 14 are gating. E is pro vided with sufiicient amplitude to furnish exactly one half the number of volt seconds which were available to the resetting cores during their gating half cycle. The magnetizing current for the resetting cores from source E flows through winding 40 of signal input transformer 41 but will have no effect upon the signal source because of the cancellation of magnetomotive forces. For the half cycle of operation shown, current from E flows through rectifiers 48 and 46 and control windings 31 and 33 but it is blocked from the other control windings by rectifiers 47 and 49. The polarity of voltage source E for the half cycle shown is selected to send current through switching rectifier 50 and limiting resistor 52 thus opening rectifier 50 to the flow of magnetizing current from voltage source E and also to the flow of cur-rent in one of windings 31 and 33 from the signal source E Signal voltage E produces a transformed voltage in winding 40 of such a polarity as to aid voltage E for one resetting core and subtract from E in the other resetting core by an equal number of volt seconds, thus establishing a differential reset of cores 11 and 13. Switching rectifiers 50 and 51 are included in series with E to decouple the gating cores from the signal voltage input transformer. Since E is a sine wave of half the volt seconds content of the transformed gating voltage, the instantaneous values of the transformed voltage in the control circuits of the gating cores will be larger than E This voltage would be of such a polarity as to cause current to flow through rectifiers 47 and 49 and upset the operation of the circuit. Voltage source E is provided with the polarity shown and sufficient value to shut ofi switching rectifier 51 when cores 12 and 14 are gating and thus prevent the flow of current in winding 40 from voltage transformed into control windings 32 or 34 when cores 12 or 14 are gating. These functions will reverse on the next half cycle of applied voltage.

The transportation of the control leads from cores 11 and 13 with respect to cores 12 and 14 is necessary to give alternating output voltage through the output coupling transformer 29. Direct connection would cause cores 11 and 12 to saturate first during alternate half cycles thus producing unidirectional current pulses through the corresponding half of coupling transformer 29. This in turn would drive the core to saturation in one direction and consequently drop the transformer out of the circuit. If reversible polarity unidirectional output current is desired, the coupling transformer 29 may be replaced with a coupling resistor and the control circuit reconnected directly. If unidirectional voltage control is desired, the signal input transformer 41 may be replaced With a high resistance coupling resistor and the signal voltage connected across the ends of the coupling resistor. This will entail a loss in efliciency in the control circuit since the coupling resistor will be in parallel with the cores across the signal source.

Although selection of component values and materials will be largely dictated by specific applications and power requirements of the amplifiers, representative embodiments of the circuits of Figs. 1 and 2 have employed "grain oriented 50% nickel, 50% iron saturable core toroids wound to saturate with 60 volts at 60 cycles applied to the gating winding. The control winding on each core was wound to saturate at half of this voltage. The material used for the supply transformers is relatively unimportant as they are acting simply as transformers. The output transformer 29 was wound on grain oriented 5% silicon iron, since the main requirement is high remanence. For the circuit in Fig. l, 1Nl51 germanium junction load rectifiers were used and the by-pass resistors were individually adjusted with the circuit in operation to give 90 reset of each core. The values of load resistance and compensating resistance for maximum power output were empirically determined with the aid of an electrodynomometer type watt meter. For the parallel feed circuit of Fig. 2, the additional rectifiers used in the control circuit were 1N93s. The input impedance for the control voltage was set at approximately 20,000 ohms by the selection of the input transformer turns ratio.

It will be understood that the circuits and specifications herein set forth are representative only and that many modifications may be made without departing from the spirit and scope of this invention which should not be limited except as defined by the appended claims.

What is claimed is:

l. A magnetic amplifier having two pairs of saturable cores having load and control windings, an output circuit having two portions, separate alternating supply sources and rectifiers for each of said load windings, an impedance means common to the series connection of each load winding with its associated rectifier and source and a portion of the output circuit, said rectifiers and sources being polarized to permit conduction in the load windings of one pair of cores on one half cycle and of the other pair of cores on the successive half cycle of the source frequency and always in the same direction through said common impedance, the load windings of each pair of cores having their respective series circuits completed through different portions of said output circuit.

2. A magnetic amplifier having two pairs of saturable cores having load and control windings, an output circuit having two portions, separate alternating supply sources and rectifiers for each of said load windings, an impedance means common to the series connection of each load winding with its associated rectifier and source and a portion of the output circuit, said rectifiers and sources being polarized to permit conduction in the load windings of one pair of cores on one half cycle and of the other pair of cores on the successive half cycle of the source frequency and always in the same direction through said common impedance, the load windings of each pair of cores having their respective series circuits completed through difierent portions of said output circuit, control signal input means connected to the control windings so as to differentially reset the cores of each pair, and means for providing a fixed reset bias to the cores independent of a control signal.

3. A magnetic amplifier having two pairs of saturable cores having load and control windings, an output circuit having two portions, separate alternating supply sources and rectifiers for each of said load windings, an impedance means common to the series connection of each load winding with its associated rectifier and source and a porb tion of the output circuit, said rectifiers and sources being polarized to permit conduction in the load windings of one pair of cores on one half cycle and of the other pair of cores on the successive half cycle of the source frequency and always in the same direction through said common impedance, the load windings of each pair of cores having their respective series circuits completed through different portions of said output circuit, control signal input means connected to the control windings so as to differentially reset the cores of each pair, and resistance means in parallel with each of said rectifiers to provide a fixed reset bias to the cores independent of a control signal.

4. A magnetic amplifier having two pairs of saturable cores having load and control windings, an output circuit having two portions, separate alternating supply sources and rectifiers for each of said load windings, an impedance means common to the series connection of each load winding with its associated rectifier and source and a portion of the output circuit, said rectifiers and sources being polarized to permit conduction in the load windings of one pair of cores on one half cycle and of the other pair of cores on the successive half cycle of the source frequency and always in the same direction through said common impedance, the load windings of each pair of cores having their respective series circuits completed through difierent portions of said output circuit, a control signal input transformer having its output connected in parallel to each of said control windings, separate rectifier means completing the parallel connections to each of said control windings, said transformer and control winding rectifiers being poled to permit conduction in a different control winding of each pair on successive half cycles of the control signal.

5. A magnetic amplifier having two pairs of saturable cores having load and control windings, an output circuit having two portions, separate alternating supply sources and rectifiers for each of said windings, an impedance means common to the series connection of each load winding with its associated rectifier and source and a portion of the output circuit, said rectifiers and sources being polarized to permit conduction in the load windings of one pair of cores on one half cycle and of the other pair of cores on the successive half cycle of the source frequency and always in the same direction through said common impedance, the load winding-s of each pair of cores having their respective series circuits completed through different portions of said output circuit, a control signal input transformer having its output connected in parallel to each of said control windings, separate rectifier means completing the parallel connections to each of said control windings, said transformer and control winding rectifiers being poled to permit conduction in a dif ferent control winding of each pair on successive half cycles of the control signal, and a fixed reset bias source for said cores, said bias source alternating synchronously with the supply source and interposed in series with the parallel connection of the control windings to the control signal transformer.

6. A magnetic amplifier having two pairs of saturable cores having load and control windings, an output circuit having two portions, separate alternating supply sources and rectifiers for each of said load vw'ndings, an impedance means common to the series connection of each load winding with its associated rectifier and source and a portion of the output circuit, said rectifiers and sources being polarized to permit conduction in the load windings of one pair of cores on one half cycle and of the other pair of cores on the successive half cycle of the source frequency and always in the same direction through said common impedance, the load windings of each pair of cores having their respective series circuits completed through different portions of said output circuit, a control signal input transformer having its output connected in parallel to each of said control windings, separate recti- 7 fier means completing the parallel connections to each of said control windings, said transformer and control winding rectifiers being poled to permit conduction in a different control winding of each pair on successive half cycles of the control signal, a fixed reset bias source for said cores, said bias source alternating synchronously with the supply source and interposed in series with the parallel connection of the control windings to the control signal transformer, a pair of switching rectifiers each disposed to complete the parallel connection between one pair of control windings and the control signal transformer, said switching rectifiers being poled to decouple the control windings of the gating cores from the control signal transformer, and a switching rectifier bias source alternating synchronously with the reset and supply sources and connected in parallel with each of the switching rectifiers and polarized to permit the flow ofcurrent from the fixed bias source to the control windings of the resetting cores.

References Cited in the file of this patent UNITED STATES PATENTS 2,126,790 Logan Aug. 16, 1938 2,629,847 Eames et al. Feb. 24, 1953 2,632,145 Sikorra Mar. 17, 1953 2,704,823 Storm Mar. 22, 1955 OTHER REFERENCES Full Wave Reversible-Polarity Half-Cycle-Response 5 Magnetic Amplifiers, by C. B. House, June 20, 1955,

NRL Report 4541. 

